III2(O2CMe)4]3[MIII

Published on Web 07/20/2002

Synthesis and Magnetic Properties of 3-D [RuII/III2(O2CMe)4]3[MIII(CN)6] (M ) Cr, Fe, Co) Yi Liao, William W. Shum, and Joel S. Miller* Department of Chemistry, UniVersity of Utah, 315 South 1400 East Room 2124, Salt Lake City, Utah 84112-0850 Received April 17, 2002

In the pursuit of new molecule-based magnets,1 the diruthenium tetraacetate cation, [RuII/III2(O2CMe)4]+ (1), is an intriguing building block. 1 has a high-spin S ) 3/2 ground state due to the accidental

χM )

Ng2µB2

[S(S + 1)]

(1)

3kB(T - θ)

with eq 1, the ruthenium(II/III) dimer is known to have a large zero-field splitting (D) and a temperature-independent paramagnetic (TIP) component, and its contribution to χ(T) can be described by eq 2;2b,6,13 eq 3 can be used to model the expected χ(T) for 2-4. The Weiss constant, θ, is introduced to roughly simulate the magnetic interactions between the paramagnetic species. degeneracy of the π* and δ* HOMOs,2 an unusually large zerofield splitting, D ) +53 ( 24 cm-1,2b,3 and the ability to add one or two ligands axial to the Ru-Ru bond. Several extended structures based on 1 have been reported.4-6 However, even when the structure is bridged with organic radicals such as nitroxides, albeit antiferromagnetically coupled, magnetic ordering does not occur.6a We report herein [RuII/III2(O2CMe)4]3[MIII(CN)6] [M ) Cr (2), Fe (3), Co (4)] and their magnetic properties, including magnetic ordering at 33 K for 2, a rare example of a magnet containing a second-row transition metal. Compounds 2-4 form upon addition of an aqueous solution of K3[MIII(CN)6] to a freshly prepared aqueous solution containing a stoichiometric amount of [RuII/III2(O2CMe)4]Cl in an inert atmosphere.7 The νCN IR spectrum shows single sharp absorptions at 2138, 2116, and 2125 cm-1 for 2-4, respectively, consistent with maintaining octahedral symmetry about the MIII site. In addition, all three compounds show characteristic asymmetric and symmetric ν(OCO) bands at 1444 and 1403 cm-1 and a δ(CO2) band at 691 cm-1 for 1.8 On the basis of the stoichiometry and ability of 1 to axially coordinate to the N of cyanide, 2-4 are proposed to form a 3-D network structure with sMsCtNsRudRusNtCsMs linkages along all three Cartesian axes, as illustrated in Figure 1. A related motif is observed for the Prussian blue family of magnetic materials.9 The powder diffraction patterns of 2-4 can be indexed10 to isomorphous body-centered cubic structures with a ) 13.34, 13.30, and 13.10 Å, respectively. On the basis of the structures of [M(CN)6]3- 11 and 1,3 the M‚‚‚M linkage separation a ≈ 13 Å and aCo < aFe < aCr are expected, as observed. Hence, the diffraction data are consistent with the structure in Figure 1. The body-centered space group indicates a second independent lattice interpenetrating the first lattice, as observed, for example for Mn[C(CN)3]2.12 The magnetic susceptibilities, χ, of 2-4 were studied using a SQUID magnetometer between 2 and 300 K. The effective moments, µeff [)(8χT)1/2] at 300 K for 2-4 are 7.72, 7.30, and 7.26 µB, respectively. These values are in good agreement for the summation of independent spins based on the Curie-Weiss equation, eq 1, i.e., 7.75, 6.93, and 6.71 µB. Modeling of µeff(T) (Figure 2) is more complex, as although the M site can be modeled * To whom correspondence should be addressed. E-mail: [email protected].

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J. AM. CHEM. SOC. 2002, 124, 9336-9337

[

Ng2µB2 1 1 + 9e-2D/kBT χRu2 ) + kB(T - θ) 3 4(1 + e-2D/kBT) 2 1 + (3kBT/4D)(1 - e 3 1 + e-2D/kBT χTot ) 3χRu2 + χM

-2D/kBT

]

)

+ TIP (2) (3)

As CoIII is diamagnetic, for T > 2 K, µeff(T) for 4 can be fit by eq 2, with D ) 69.4 cm-1, TIPRu2 ) 800 × 10-6 emu/mol, θ ) 0 K, gRu2 ) 2.04, and the chi-squared agreement factor14 is ∑(µexp µcalc)2/µexp ) 2.823 × 10-3 (Figure 2). This is in accord with magnetic behavior observed for several other complexes containing 1.6 In contrast to the case for 4, eq 3 fits µeff(T) only above 120 and 8 K for 2 and 3, respectively (Figure 2). For 2, the data can be fit with D ) 69.4 cm-1, θ ) -40 K, gRu2 ) 2, gFe ) 2, and TIPRu2 ) 700 × 10-6 emu/mol (chi-squared ) 5.511 × 10-3). The fitting parameters indicate significant antiferromagnetic coupling between adjacent spin sites. Upon decreasing T for 2, µeff(T) increases below ∼50 K, reaching a maximum value of 30.9 µB at 32 K prior to abruptly decreasing to 3.65 µB at 2 K (Figure 2).

Figure 1. Proposed 3-D body-centered, interpenetrating network structure for [Ru2(O2CMe)4]3[MIII(CN)6] (M ) Cr, Fe, Co); the bridging acetates, rotated 45° with respect to [MIII(CN)6]3-, are not shown for clarity. 10.1021/ja020552c CCC: $22.00 © 2002 American Chemical Society

COMMUNICATIONS

Figure 2. µeff(T) and the fit to the higher temperature data with eqs 2 and 3 for 2 (top) and 3 and 4 (bottom).

leads to a small increase in M, which for a metamagnet increases above ∼800 Oe prior to saturation. Hysteresis with a very unusual constricted shape is observed at 2 K (Figure 3b). The remanent magnetization at 2 K is 3700 emu‚Oe/mol. Constricted hysteretic behavior and reduced Ms have been attributed to metamagnetism caused by canted spins,11b and this phenomenon is under further study. Above 8 K, µeff(T) for 3 can be fit by eq 3 (Figure 3). The data can be fit with D ) 69.4 cm-1, θ ) 0.7 K, gRu2 ) 2.075, gFe ) 2, and TIPRu2 ) 400 × 10-6 emu/mol (chi-squared ) 2.448 × 10-3). The divergence at 8 K suggests a transition from short-range ferromagnetic interaction to long-range magnetic ordering. Upon decreasing T for 3, µeff(T) increases sharply at ∼10 K, reaching 19.2 µB at 2 K (Figure 3). χ′(T) and χ′′(T) increase with decreasing temperature, but peaks are not present above 2 K. These data suggest that the onset of magnetic ordering occurs below 2 K. These initial studies show that 1 can be used as a building block for the formation of molecule-based magnets. Acknowledgment. The authors gratefully acknowledge partial support from the U.S. National Science Foundation (Grant No. CHE 0110685), the Air Force Office of Scientific Research (Grant No. F49620-00-1-0055,) U.S. DOE (Grant No. DE FG 03-93ER45504), and the ACS PRF (Grant No, 36165-AC5). References

Figure 3. (a) Alternating current χ′(T) and χ′′(T) at 9.9, 99, and 999 Hz. (b) M(H) showing a constricted hysteresis loop for 2.

This behavior is indicative of magnetic ordering. To confirm that 2 magnetically orders, the in-phase (χ′) and out-of-phase (χ′′) alternating current susceptibilities were taken and show frequencyindependent peaks for both χ′(T) at 32 K and χ′′(T) at 34 K, confirming that 1 orders with Tc ) 33 ( 1 K (Figure 3a). The field dependence of the magnetization, M(H), approaches saturation at 2 kOe and saturates to a value of 17 870 emu‚Oe/mol at 2 K (Figure 3b). Assuming g ) 2, a saturation magnetization, Ms, of 67 000 emu‚Oe/mol is expected for ferromagnetic coupling, while a value of 33 500 emu‚Oe/mol is expected for antiferromagnetic coupling. Antiferromagnetic coupling as observed for the 1-D chain of 1(NITPh) (NITPh ) phenyl nitronyl nitroxide),6a leading to ordering as a ferrimagnet, is expected for 2. The observed value is one-half the expectation for the latter, and this low value may be due to the large D of the ruthenium dimer, since for T , D, only the S ) 1/2 state is significantly populated at 2 K. An applied field

(1) (a) Ovcharenko, V. I.; Sagdeev, R. Z. Russ. Chem. ReV. 1999, 68, 345. Day, P. J. Chem. Soc., Dalton Trans. 1997, 701. Miller, J. S.; Epstein, A. J. Chem. Eng. News 1995, 73 (40), 30. Miller, J. S.; Epstein, A. J. AdV. Chem. Ser. 1995, 245, 161. Miller, J. S.; Epstein, A. J. Angew. Chem., Int. Ed. Engl. 1994, 33, 385. (b) Miller, J. S.; Epstein, A. J. Chem. Commun. 1998, 1319. (2) (a) Norman, J. G., Jr.; Renzoni, G. E.; Case, D. A. J. Am. Chem. Soc. 1979, 101, 5256. (b) Miskowiski, V. M.; Hopkins, M. D.; Winkler, J. R.; Gray, H. B. In Inorganic Electronic Structure and Spectroscopy; Solomon, E. I., Lever, A. B. P., Eds.; John Wiley & Sons: New York, 1999; Vol. 2, Chapter 6. (3) Telser, J.; Drago, R. S. Inorg. Chem. 1984, 23, 3114. Cukiernik, F. D.; Giroud-Godquin, A. M.; Maldivi, P.; Marchon, J. C. Inorg. Chim. Acta 1994, 215, 203. Handa, M.; Sayama, Y.; Mikuriya, M.; Nukada, R.; Hiromitsu, I.; Kasuga, K. Bull. Chem. Soc. Jpn. 1998, 71, 119. JimenezApraricio, R.; Urbanos, F. A.; Arrieta, J. M. Inorg. Chem. 2001, 40, 613. (4) Beck, E. J.; Drysdale, K. D.; Thompson, L. K.; Li, L.; Murphy, C. A.; Aquino, M. A. S. Inorg. Chim. Acta 1998, 279, 121. (5) Cotton, F. A.; Lu, J.; Yokochi, A. Inorg. Chim. Acta 1998, 275-276, 447. Cotton, F. A.; Kim, Y.; Ren, T. Inorg. Chem. 1992, 31, 2723. Cotton, F. A.; Kim, Y.; Ren, T. Polyhedron 1993, 12, 607. Cotton, F. A.; Matusz, M.; Zhong, B. Inorg. Chem. 1988, 27, 4368. (6) (a) Handa, M.; Sayama, Y.; Mikuriya, M.; Nukada, R.; Hiromitsu, I.; Kasuga, K. Chem. Lett. 1996, 201. Sayama, Y.; Handa, M.; Mikuriya, M.; Hiromitsu, I.; Kasuga, K. Chem. Lett. 1998, 777. (b) Handa, M.; Sayama, Y.; Mikuriya, M.; Nukada, R.; Hiromitsu, I.; Kasuga, K. Bull. Chem. Soc. Jpn. 1995, 64, 1647. (7) After the solution was stirred for 2 h, the product was collected by filtration and dried in a vacuum. Once separated, the products are stable in air. Elemental analysis gave satisfactory results. (Calcd for 2: C, 23.66; H, 2.38; N, 5.52. Obsd: C, 23.82; H, 2.48; N, 5.72. Calcd for 3: C, 23.60; H, 2.38; N, 5.50. Obsd: C, 23.68; H, 2.41; N, 5.14. Calcd for 4: C, 23.55; H, 2.37; N, 5.49. Obsd: C, 23.37; H, 2.13; N, 5.28.) (8) Drysdale, K. D.; Beck, E. J.; Cameron, T. S.; Robertson, K. N.; Aquino, M. A. S. Inorg. Chim. Acta 1997, 256, 243. Miskowiski, V. M.; Gray, H. B. Inorg. Chem. 1988, 27, 2501. (9) E.g.: Mallah, S.; Thiebaut, S.; Verdauguer, M.; Veillet, P. Science 1993, 262, 1554. Ferlay, S.; Mallah, T.; Ouahes, R.; Veillet, P.; Verdauguer, M. Nature 1995, 378, 701. Entley, W. R.; Girolani, G. S. Inorg. Chem. 1994, 33, 5165. (10) CMPR distributed by NIST: http://webster.ncnr.nist.gov/programs/crystallography/software/cmpr/ (11) E.g.: (a) Ohba, M.; Usuki, N.; Fukita, N.; Okawa, H. Inorg. Chem. 1998, 37, 3349. Ferlay, S.; Mallah, T.; Vaissermann, J.; Bartolome, F.; Veillet, P.; Verdauguer, M. J. Chem. Soc., Chem. Commun. 1996, 2481. Re, N.; Crescenzi, R.; Floriani, C.; Miyasaka, H.; Matsumoto, N. Inorg. Chem. 1998, 37, 2717. Lu, J.; Harrison, W. T. A.; Jacobson, A. J. J. Chem. Soc., Chem. Commun. 1996, 399. (b) Ohba, M.; Okawa, H.; Fukita, N.; Hashimoto, Y. J. Am. Chem. Soc. 1997, 119, 1011. (12) Manson, J. L.; Campana, C.; Miller, J. S. J. Chem. Soc., Chem. Commun. 1998, 251. Miller, J. S. AdV. Mater. 2001, 13, 525. (13) (a) O’Connor, C. J. Prog. Inorg. Chem. 1982, 29, 203. (b) Telser, J.; Drago, R. S. Inorg. Chem. 1985, 24, 4765. (14) Taylor, J. R. An Introduction to Error Analysis; University Science Books: Mill Valley, CA, 1982; p 223.

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